Given the following string:

let str = '为中华\n\n只崛aaa起\n而读书\n     我是123中国1111人';

Desired Formatting Effects

• Auto-indent with 4 spaces after each line break
• Add spacing between numbers and other characters
• Add spacing between letters and other characters
• Idempotent formatting (repeated formatting won’t cause inconsistencies)

Implementation code:

// Lookahead assertion to ensure no 4 spaces follow
const brReg = /\n(?!\s{4})/g;
// Lookbehind assertion to check preceding characters
const numPreReg = /(?<!\s|\d)(\d+)/g;
const numExtReg = /(\d+)(?!\s|\d)/g;
const charPreReg = /(?<!\s|[a-zA-Z])([a-zA-Z]+)/g;
const charExtReg = /([a-zA-Z]+)(?!\s|[a-zA-Z])/g;

str = str.replace(brReg, '\n    ');
str = str.replace(charPreReg, ' $1');
str = str.replace(charExtReg, '$1 ');
str = str.replace(numPreReg, ' $1');
str = str.replace(numExtReg, '$1 ');

// Output: 为中华\n    \n    只崛 aaa 起\n    而读书\n     我是 123 中国 1111 人
console.log(JSON.stringify(str));

PS: This formatting logic powers YouMengJi's automatic text formatting feature